OpenGL video performance

Michel Dänzer michel at
Thu May 3 00:31:22 PDT 2012

On Mit, 2012-05-02 at 20:09 +0200, Greg G. wrote: 
> On 01.05.2012 09:49, Michel Dänzer wrote:
> > On Fre, 2012-04-27 at 17:21 +0200, Greg G. wrote:
> >> What I keep thinking about: could there any problem arise from the way
> >> the driver allocates VRAM? Can there be resource conflicts, effectively
> >> limiting the GL troughput only be cause some memory is already used, for
> >> example by EXA?
> >
> > In theory yes, but only if the working sets of all running apps exceed
> > the amount of VRAM, which is unlikely for the scenarios you've
> > described.
> As a follow up to this, I just browsed through an older thread on the 
> mythtv-users list discussing the same issue. Quoting from the following 
> post of one of the mythtv devs:
> ------------ quote
> You have to bear in mind that the single biggest bottleneck for OpenGL
> deinterlacing performance is texture sampling.
> When no deinterlacing is taking place, there is one texture sample per
> pixel (we do some packing of the video frame data in software before
> sending it to the gpu to avoid sampling for the luma and both
> chromas).
> When you are using the OpenGL kernel deinterlacer, there are 8 texture
> samples for each pixel in the frame. Depending on your gpu, gpu memory
> type and speed, video resolution etc, this may simply be too slow. You
> may not be using the cpu to perform deinterlacing, but the gpu still
> has a finite time to complete the process before the frame needs to be
> displayed.
> ------------ /quote
> Perhaps mythtv _is_ overly using resources? Could I try any xorg.conf 
> setting to shift resource management towards favouring opengl?

No, and the above refers to an increase in memory bandwidth needed, not
storage. Your GPU is either fast enough or it isn't. Have you tried
disabling the deinterlacing or tested with non-interlaced videos to see
if it makes a difference?

Earthling Michel Dänzer           |         
Libre software enthusiast         |          Debian, X and DRI developer

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